1. Technical Field
The present invention relates to electric rotating machines that are used in, for example, motor vehicles as electric motors and electric generators. In addition, the invention can also be applied to industrial machines and household electrical appliances.
2. Description of Related Art
Conventionally, there are known electric rotating machines which include an annular stator core (or armature core) and a multi-phase stator coil (or armature coil) that is comprised of a plurality of phase windings wound on the stator core.
Further, for securing electrical insulation between the phase windings, the stator coil is formed of a plurality of insulation-coated electric wires each of which has an insulating coat formed at the surface thereof (see, for example, Japanese Patent Application Publication No. 2008-54404).
Moreover, there are also known methods of winding the stator coil on the stator core, such as concentrated winding and distributed winding methods.
In general, a distributed winding method is preferable to a concentrated winding method in terms of securing high torque. However, when the stator coil is wound on the stator core using a distributed winding method, the phase windings may overlap each other at coil end parts of the stator coil; the coil end parts respectively protrude from opposite axial end faces of the stator core. Consequently, unlike in the case of winding the stator coil using a concentrated winding method, it may become difficult to reliably secure electrical insulation between the phase windings.
To solve the above problem, one may consider increasing the thickness of the insulating coats of the electric wires forming the stator coil, thereby preventing puncture (or breakdown) of the insulating coats from occurring due to partial discharge between the phase windings.
However, on the other hand, with the increase in the thickness of the insulating coats, the space factors of the electric wires in slots of the stator core will be lowered.
In particular, when the electric rotating machine is a high-voltage machine, it is especially difficult to secure electrical insulation between the phase windings by increasing the thickness of the insulating coats while preventing the space factors of the electric wires in the slots from being lowered.